DragonFlyBSD

:DragonFly won't let me zero a partition:
:
:zoot# dd if=/dev/zero of=/dev/ad8s2d
:dd: /dev/ad8s2d: Read-only file system
:1+0 records in
:0+0 records out
:0 bytes transferred in 0.000135 secs (0 bytes/sec)
:
:Sascha
:
:--
:http://yoyodyne.ath.cx

That is the error you usually get if the partition in question is
    still mounted.

-Matt
                    Matthew Dillon 
                    <dillon@backplane.com>

Yeah but it isn't.

zoot# mount | grep ad8s2d
zoot# dd if=/dev/zero of=/dev/ad8s2d
dd: /dev/ad8s2d: Read-only file system
1+0 records in
0+0 records out
0 bytes transferred in 0.009650 secs (0 bytes/sec)

Sascha

:...
:>
:> That is the error you usually get if the partition in question is
:> still mounted.
:
:Yeah but it isn't.
:
:zoot# mount | grep ad8s2d
:zoot# dd if=/dev/zero of=/dev/ad8s2d
:dd: /dev/ad8s2d: Read-only file system
:1+0 records in
:0+0 records out
:0 bytes transferred in 0.009650 secs (0 bytes/sec)
:
:Sascha
:
:--
:http://yoyodyne.ath.cx

That's odd.  Is /dev or / mounted read-only?  What about the modes
    on /dev/ad8s2d ?   If you do a fresh boot (i.e. never having tried to
    mount anything using that device), and then issue the dd, does it
    work differently?

Does disklabel recognize the disk?

Also try regenerating the /dev entry for ad8s2.

cd /dev
    ./MAKEDEV ad8
    ./MAKEDEV ad8s2
    ./MAKEDEV ad8s2a

-Matt
                    Matthew Dillon 
                    <dillon@backplane.com>

Hmm,

I tried most of this, all negative.

However, I do have some partitions of the ad8s1 slice mounted (/,
/usr, etc.). Could it be because of this? I would think this shouldn't
affect partitions on ad8's other slices, right?

I'll try later from a LiveCD.

Sascha

:> on /dev/ad8s2d ? If you do a fresh boot (i.e. never having tried to
:> mount anything using that device), and then issue the dd, does it
:> work differently?
:>
:> Does disklabel recognize the disk?
:>
:> Also try regenerating the /dev entry for ad8s2.
:>
:> cd /dev
:> ./MAKEDEV ad8
:> ./MAKEDEV ad8s2
:> ./MAKEDEV ad8s2a
:
:Hmm,
:
:I tried most of this, all negative.
:
:However, I do have some partitions of the ad8s1 slice mounted (/,
:/usr, etc.). Could it be because of this? I would think this shouldn't
:affect partitions on ad8's other slices, right?
:
:I'll try later from a LiveCD.
:
:Sascha

Is this on 1.12 or HEAD ?  I do recall a bug in the partition-open
    bitmap in the disk layer that I'm pretty sure I fixed in HEAD, but
    may not have fixed in 1.12.  It is possible there is an issue there,
    it is worth checking out.

-Matt
                    Matthew Dillon 
                    <dillon@backplane.com>

It's on HEAD. I just booted with last night's snapshot and the problem
is the same, so it doesn't seem to matter whether other partitions on
the same disk are mounted or not.

Sascha

:It's on HEAD. I just booted with last night's snapshot and the problem
:is the same, so it doesn't seem to matter whether other partitions on
:the same disk are mounted or not.
:
:Sascha
:
:--
:http://yoyodyne.ath.cx

Post the disklabel output.  If partition 'd' starts at offset 0
    you won't be able to dd into it, because it will overlap the disklabel
    itself (which is protected).

Matthew Dillon 
                    <dillon@backplane.com>

Hmm,

this seems to be the cause here:

1. /dev/ad8s2:
   type: unknown
   disk: amnesiac
   label:
   flags:
   bytes/sector: 512
   sectors/track: 57
   tracks/cylinder: 117
   sectors/cylinder: 6669
   cylinders: 20473
   sectors/unit: 136534437
   rpm: 3600
   interleave: 1
   trackskew: 0
   cylinderskew: 0
   headswitch: 0 # milliseconds
   track-to-track seek: 0 # milliseconds
   drivedata: 0

1. size offset fstype
   c: 136534437 0 unused # 66667.206MB
   d: 136534437 0 4.2BSD # 66667.206MB

Sascha

:Hmm,
:
:this seems to be the cause here:

Yup, that's the problem.  I should have thought of it sooner.
    Basically it has to work this way.  It is an artifact of the BSD
    label's in-band storage of the label.  GPT labels store the actual
    label out-of-band, so that sort of problem doesn't crop up.

But with BSD disklabels, the disklabel itself is stored in-band, meaning
    at sector 0 as displayed by the label.  To avoid it is best to start
    at sector 16.

You can zero out the disk slice using e.g. ad8s2 (which is access without
    going through the label and thus is able to overwrite the label), but
    if you access it via a partition in the label and the partition starts
    at sector 0, e.g. ad8s2d, then that chunk at the beginning containing
    the label itself will be read-only by default.

-Matt

Hmm, unfortunately, using ad8s2 alone gives the same result:

zoot# dd if=/dev/zero of=/dev/ad8s2
dd: /dev/ad8s2: Read-only file system
1+0 records in
0+0 records out
0 bytes transferred in 0.003719 secs (0 bytes/sec)

disklabel -W ?

Actually I almost removed -W / -N flags from disklabel(8) some time ago,
as I did understand from Matts commit messages that this was removed;
I found out that these flags are still working though.
Must have misread commit messages & and didn't read the code.

On similar lines: it seems like it is neede to reboot DragonFly
when changing between 32-bit and 64-bit disklabels, can this be correct?
After erasing a disklabel (eg 32-bit), using dd, disklabel64 fails,
as kernel still have copy of 32-bit disklabel.

-thomas

can we close this? seems like "we'll, that's how it is"